The blind Chinese activist Chen Guangcheng has said he fears his nephew may be beaten and tortured after being detained by police.

Although Chen was confident last week's high-level deal between China and the US would ensure his own wellbeing and freedom of movement, he told the Guardian he was concerned about the vulnerability of his relatives because of the "lawlessness" of his home province of Shandong.

The activist, who escaped from house arrest and initially fled to the US embassy last month, is now recuperating in a Beijing hospital.

But it has emerged that his nephew, Chen Kegui, is being investigated in connection with a bloody fight that broke out when local officials tried to enter the family home in Linyi, in Shandong province, after the escape.

The nephew previously said he stabbed one of the intruders in an act of self-defence. His lawyer, Liu Weiguo, who is being closely monitored by the police, said he was unable to talk freely about the case, which was still under investigation, but he feared the arrests of family members could hinder Chen's departure.

"It is hard to know how the local authorities will act as they do not seem to behave rationally," Liu said. "But if more family members are arrested, it will be less likely that Chen can go abroad. Maybe he will end up stuck in China." Chen said he was unaware of his nephew's condition, but his own experience in Linyi had taught him to fear the worst.

"My nephew certainly can't be in good condition in their hands. He'll certainly be tortured there … The public security organs, procuratorial organs and people's courts are absolutely lawless in Shandong province."

The treatment of Chen's relative and supporters has been mixed. He Peirong, the activist who drove Chen from Shandong to Beijing, has been released from police detention but ordered not to give interviews, and is likely to be under tight surveillance.

Chen said he had not been allowed to see his own lawyers, and expressed grief at reports that one of them – Jiang Tianyong – had been beaten. His own access to information is limited because diplomats, journalists and friends have been unable to go freely into his hospital room.

Another friend, Zeng Jinyan has been put under tighter restrictions since last Wednesday, and is now allowed out only to take her daughter to nursery school and to collect her.

Zeng revealed at the weekend that the police have also repeatedly denied her request to leave mainland China so that she can take up a university place in Hong Kong. "Last year, I began to talk to police about my study plans," she tweeted. "But until now, the result is always the same: they won't let me go."

Chen, in contrast, feels that he has a public, high-level assurance that he can leave to study. At the end of last week, he was offered a fellowship in the US, and the Chinese foreign ministry said he could apply for travel documents.

These guarantees remain somewhat ambiguous. Along with critical commentaries in the domestic media that accuse Chen of stirring up trouble in his home village over a UK-funded well that he helped to arrange, the vague words have prompted scepticism that the state will allow Chen to leave.

But the activist was optimistic the central government authorities would honour the arrangement.

"There may be a few obstacles, but I believe it will work out OK. They agreed to let me go abroad in full public view. They should let me go. This is my civil right," he said.

Asked whether he would like journalists and diplomats to visit him before he leaves, he was clear: "Generally, I like to interact with people – any people."